The present invention relates to a system for searching a position on a magneto-optical recordable disc such as a Minidisc, and more particularly to a track search system.
A compact disc (CD) is well known as a recording medium for audio signal information. There are two types of the CDS, one type of which has the diameter of 12 cm and the other type has the diameter of 8 cm. Information is recorded on the CD for 74 minutes at maximum in the form of a digital signal.
To the contrary, the Minidisc (MD) which is smaller than the CD (the diameter is 6.4 cm), which has the same reproducing time as the CD, and which is capable of writing and rewriting has become popular.
Although the MD has the small diameter, it is possible to record and reproduce data for 74 minutes by using a data compression technique. Furthermore, in the MD, a shock proof memory (DRAM) is provided for preventing an audio signal from being interrupted which is caused by a jump of a pickup.
Supposing that the capacity of the DRAM is one Mbit, while the MD is played, the DRAM becomes full in 0.9 second. When a jump of the pickup occurs, it becomes impossible for the pickup to read the data. Since the data stored in the DRAM is applied for another three seconds, if the pickup quickly returns to the position where the data are not read in three seconds and resumes the reading, there is no interruption in the audio signal fed to the loudspeaker.
The MD has a standard linear velocity determined in a range between 1.2 and 1.4 m/s which is the same as the CD.
An MD player is provided with a ROM storing data of addresses of recorded information. The data are divided into clusters which are units for recording the information. The clusters are determined based on the linear velocity. The ROM has a table storing data representing the relationship between the cluster and the track of the disc, which is used for searching a desired track.
In such an MD player, if the track search of an MD having the linear velocity of 1.2 m/s is performed in accordance with a table made based on the linear velocity of 1.4 m/s, the pickup jumps the track in accordance with the data based on the linear velocity of 1.4 m/s. Such jumping causes a large deviation of the pickup position from the desired track. The pickup must be moved to a cluster of the desired track. Accordingly, the time for searching the desired track is elongated.